I'll be throwing up some of these strategy guides for Horde mode based on when I play whatever map for an extended period of time. Here is my first one for Security.
Also, be sure to post any strategies and tips you've used that seem to work great too!
Starting off, it is imperative to set up in the "laser cage" where the Mulcher and Mortar spawn. Those two weapons are blocked off from the rest of the map by laser walls that gib any Locust that walks through them (and they do walk through them, which is absolutely hilarious to watch). The best thing to do is immediately run there and start getting ready. Grab the Mulcher and set it up on the sandbag that faces the middle of the map. This can provide lots of cover while the lasers come online for any Locust that spawn back in the Sniper/Flamethrower area. Off the beginning you'll also want to grab the Ink grenades and tag them to the first wall before the side laser doors. This will serve as an alert for you as to which way an enemy is coming, if their approach is unspotted.
After the lasers activate, all you basically have to do is set up watching the two side passages and middle. I recommend having the first Mulcher guy watching everything in front. He can see both staircases (which are typically where the Locust approach from - I've rarely seen one approach from middle), as well as into the middle building. Have two other guys watching the side passages, with two others posted in front at the walls looking toward middle. They can pop out as necessary to put shots on anybody, as well as help out as needed with each side passage.
This setup here is pretty much unbreakable from what I've experienced. Granted the lasers do randomly deactivate, but only for a short while, and with the superior weaponry that spawns there (the Mulcher, which is almost insta-gib) and a little team shooting, you can hold out until the lasers pop back effectively. This is also the safest setup that I know of. With the amount of cover, protection from the lasers, and superior weapons that spawn there, we never had one guy get downed the entire time we played (we played to 19 - would have gone longer but it was 3:00 a.m.) on Normal (it was also only 4 people, so I adjusted the setup to how it would work with 5 people above).
Another advantage to this setup is the fact that the Locust 99% of the time approach from the side passages. The good part about this is, once the round is over, this makes it VERY easy to just deactivate the wall, walk out a ways, and scrounge up some cool weapons and ammo. Also, as a little side note, placing Boomshields in front of the laser walls adds even more protection, specifically when the laser walls deactivate.
In regards to the Mortar (when it spawns), it is also a great weapon to use. For instance, you can spam the courtyards between the stairs and the side entrances to where you're at with mortars, owning everything that tries to come that way. Likewise you can hit the stage across the way where Locust like to sit and Wretches/Tickers/Sires like to get caught up on. The Mortar can cover a large portion of the map, especially in the hands of an experienced person.
Also, if you conserve ammo with the mulcher and wait long enough, you can actually have three of them to cover all three entrances (which is awesome).
Although I personally love, love, love the new Hammerburst, this setup and map probably isn't the best place for it. It has its success here, but the Lancer's probably better for defense in the side passages.
This is currently my absolute most favorite map for Horde so far. It gives a real "Alamo" feeling to it and is probably one of the easiest, if not the easiest map to get to Wave 50 on that I've experienced thus far. Even if you're not worried about getting to Wave 50, it provides a ton of fun and a lot of great memories.
Grade: A